The present invention relates in general to electrical power systems, and particularly, to diagnostic services for electrical power transformers.
In the deregulated power industry there will be more demand for diagnostic services of electrical equipment, such as electrical power transformers. Many of these diagnostic services currently require that the electrical equipment (e.g., the transformer) be shut off and be out of service and this is costly to the power company. Exemplary diagnostic services that can be used to identify early warning of potential failures of power transformers are partial discharge (PD) and frequency response. However, conventional techniques for performing diagnostic services typically require that the electrical power equipment be shutdown and taken off-line in order to perform the required diagnostic services.
Electrical pre-breakdowns within electrical power equipment can lead to proliferation of chemical and mechanical destruction of insulation parts and, if not corrected, these electrical pre-breakdowns can eventually lead to equipment failure. Although numerous preventive measures are taken to decrease the probability of these internal events, electrical pre-breakdowns are still present in electrical power equipment.
For example, partial discharge (PD) is an initial component of electrical pre-breakdown and is typically accompanied by acoustic events. This phenomenon serves as a basis for several conventional acoustical techniques of detecting and locating electrical discharges. However, these conventional techniques for determining the location of electrical discharge events typically require that the electrical power equipment, such as a power transformer, be shut-down and taken out of service in order to perform the required diagnostic test and/or measurement.
As can be appreciated, conventional diagnostic services for detecting the probability of internal events leading to the breakdown of electrical power equipment are very intrusive and are expensive due to the fact that the electrical equipment is shut-down and taken off-line to accomplish the necessary diagnostic services. This creates a burden on operators to shut the equipment down and take it out of service and also increases equipment down time and thus costs. Therefore, a need exists for a new precise and simple process for performing diagnostic services to detect potential internal failures in electrical power equipment without shutting the equipment down or taking the equipment out of service.
The present invention is directed to an apparatus, system, and method for the performing diagnostic services on electrical power equipment, such as a power transformer, using a tap switch installed into each phase of the power transformer that allows the diagnostic service to be performed while the power transformer is operating and on-line.
The apparatus includes a mount-on type tap switch for connecting a piece of test and measurement equipment to an electrical power transformer and that allows a diagnostic service to be performed on the electrical power transformer while the transformer is operating and on-line. The tap switch includes a first switch and a second switch for selectively switching the tap switch between a non-diagnostic position wherein the tap switch connects the transformer to ground and a diagnostic position wherein the tap switch connects the transformer to the test and measurement system.
In the non-diagnostic position, the first switch is closed and the second switch is open. To switch to the diagnostic position, the second switch is closed and then the first switch is opened. To switch back to the non-diagnostic position, the first switch is closed and then the second switch is opened. Preferably, at least one of the first and second switches is closed at all times in order to prevent sparking across the bushing tap. Also, the test and measurement equipment is preferably terminated from the bushing tap by a capacitive coupling.
The tap switch is disposed between and selectively forms an electrical connection between the power transformer and the test and measurement system so that an applicable diagnostic service(s) can be performed on the live, on-line transformer.
In accordance with another embodiment of the invention, a system for performing a diagnostic service on live, in-service electrical power equipment includes an electrical power transformer, a tap switch, and a test and measurement system. The power transformer includes one or more phases and a bushing tap for each phase. A tap switch is coupled to each phase through the bushing tap. The tap switch includes a first switch and a second switch for selectively switching between ground (e.g., the non-diagnostic position) and a test and measurement position (e.g., the diagnostic position). The test and measurement system allows a test and measurement device to be connected to the transformer through the tap switch for performing a diagnostic test and/or measurement on the transformer.
Preferably, the transformer includes a large size power transformer having medium power and above. Preferably, the power transformer is a three-phase transformer.
Preferably, the tap switch is mounted on the transformer housing and includes an input lead for coupling the tap switch to the bushing tap of the transformer and an output lead for coupling the tap switch to the test and measurement system.
Preferably, the test and measurement system includes connections for allowing various test and measurement devices to be detachably coupled to the test and measurement system for the collections of data indicative of a condition of the transformer.
Exemplary diagnostic services that can be performed on the live, in-service transformer using the tap switch include one of a partial discharge and frequency response test and measurement.
In accordance with another embodiment of the invention, a method for performing on-line diagnostic services is provided using a tap switch comprising the steps of: installing a tap switch into each phase of a power transformer, connecting a test and measurement system to the tap switch; switching the tap switch from a non-diagnostic position to a diagnostic position; performing a diagnostic service on the transformer; switching the tap switch from the diagnostic position to the non-diagnostic position; wherein the transformer is live and on-line during the performance of the diagnostic service.
The method further includes providing a first switch and a second switch in the tap switch arranged in a parallel configuration, wherein the first switch is open when the second switch is closed and vice versa; connecting an input of the tap switch to a bushing tap at each phase of the power transformer; connecting an output of the tap switch to a test and measurement system used to perform the diagnostic services; selectively switching between a diagnostic position and a non- diagnostic position by closing and opening the first switch and/or the second switch of the tap switch.
In accordance with another aspect of the invention, wherein the method further includes the step of collecting data regarding a pre-breakdown condition of the power transformer using a test and measurement device connected to the test and measurement system.
In accordance with another aspect of the invention, the method further includes performing one of a partial discharge and a frequency response test.
Other features of the invention are described below.